Memo to the wise -- don't regulate the power supply rail of the output stage (particularly with an LM317/LM337).
Power amplifier ic's already have not bad psrr , you may hear hum with unregulated supplies ,but not loud . Another reason is power waste by regulator.
Exactly, even the LM1875 PSRR is 90dB, and you're turning potential music power into continuous heat.
Regulation of power supplies by itself is not bad idea ,but method / implementation should be different. Very low drop regulator preferred , and reduce transformer voltages first.
Here's how Douglas Self summarizes the subject in his book - Audio Power Amplifier Design Handbook, 5th Ed,. page 269
"The generic amplifier designs examined in this book have excellent supply-rail rejection, and
so a simple unregulated supply is perfectly adequate. The use of regulated supplies is definitely
unnecessary, and I would recommend strongly against their use. At best, you have doubled the
amount of high-power circuitry to be bought, built, and tested. At worst, you could have intractable
HF stability problems, peculiar slew-limiting, and some expensive device failures."
"The generic amplifier designs examined in this book have excellent supply-rail rejection, and
so a simple unregulated supply is perfectly adequate. The use of regulated supplies is definitely
unnecessary, and I would recommend strongly against their use. At best, you have doubled the
amount of high-power circuitry to be bought, built, and tested. At worst, you could have intractable
HF stability problems, peculiar slew-limiting, and some expensive device failures."
Everyone missed some important information - what is LM317 input voltage ? In other words ,how big voltage drop is on regulator.
Also i see in op's picture ,he is powering amplifier from SMPS. At best would be to directly decrease smps output voltage to required one (32v) by adjusting potentiometer (if available) or changing feedback resistor .Most smps are already regulated and double mains frequency ripple present at output only at maximum load ,when not much room left for regulation .Then replace LM317 (32V) with LC filter to remove possible HF ripple .But leave another regulator for preamp .
Also i see in op's picture ,he is powering amplifier from SMPS. At best would be to directly decrease smps output voltage to required one (32v) by adjusting potentiometer (if available) or changing feedback resistor .Most smps are already regulated and double mains frequency ripple present at output only at maximum load ,when not much room left for regulation .Then replace LM317 (32V) with LC filter to remove possible HF ripple .But leave another regulator for preamp .
If power supply voltage with load and no load are very close ,i would name that closer to "regulated" ,in opposite to big mains low frequency transformer - diode bridge - big capacitor type psu .But yes ,there exists smps , whose just generating square wave with constant duty cycle about 50% and output rectified and smoothed , no feedback - no regulation .
Really? We have hundreds in service where I work... from dozens of worldwide manufacturers, and all are regulated, as specified in the data sheets. In fact, I have never seen one that wasn't. Anyway, these are smaller (50W to 1000W range) commercial/industrial power supplies, so I can't speak for the consumer stuff, other than the PC supplies. Please enlighten me. Thanks.
I think regulating is a great idea. It not only provides a stable voltage but gives you some goof protection. Essential if you are a learner. I would make sure the LM317s have enough voltage headroom and heat dissipation, of course.
But if we return to op's schematic - power source is smps ,they always have ripple ,which better to filter out . But lm317 is old and probably slow voltage regulator ,which can't handle such high frequency ripple ,and probably will pass it partially. I think benefit is in question . For 100 or 120 hz psu ripple lm317 would work much better.